Introduction to Biology

The Science of Life

Biology is the scientific study of life and living organisms. It seeks to understand the fundamental processes that define living systems, from the molecular to the ecosystem level. Scientists and philosophers have proposed several definitions of life, but all emphasize the capacity for self-sustained chemical processes, evolution, and information storage.

• Life is a self-sustained chemical system capable of undergoing Darwinian evolution.

• Life is a self-replicating, evolving system based on organic chemistry.

• Life distinguishes a vital and functional being from a dead body.

Properties of Life

Essential Characteristics

All living things share a set of fundamental properties that distinguish them from non-living matter. These properties are supported by specific biomolecules and cellular structures.

• Membrane delimited: Living things are separated from their environment by membranes.

• Cellular organization: All life is made up of cells.

• Information storage and transmission: Life stores and follows genetic instructions.

• Energy transformation: Life stores and uses energy to perform work.

• Self-replication: Life can reproduce itself.

• Response to environment: Life controls its functions and responds to external stimuli.

• Evolution: Life evolves over generations.

Examples and Exceptions

• Mature Red Blood Cells: These cells lack DNA, do not divide, and have no mitochondria, yet are considered alive as part of a living organism.

• Mule: A mule is a hybrid animal that cannot reproduce, but is still considered alive because it meets other criteria of life.

Biomolecules Supporting Life

Main Classes of Biomolecules

Four major classes of biomolecules support the properties of life:

• Lipids: Form membranes, store energy, and provide insulation.

• Carbohydrates: Serve as energy sources and structural components.

• Nucleic Acids: Store and transmit genetic information (DNA, RNA).

• Proteins: Catalyze reactions, provide structure, and regulate processes.

Nucleic Acids: Information Storage and Transmission

Nucleic acids, such as DNA and RNA, are responsible for storing and transmitting genetic information. DNA encodes instructions for building proteins, while various forms of RNA (mRNA, tRNA, rRNA) are involved in protein synthesis.

Lipids: Membrane Structure and Function

Lipids are essential for forming biological membranes, which create compartments within cells and provide a selectively permeable barrier. Their hydrophobic properties make them ideal for this role. Lipids also serve as energy reserves and insulation.

Carbohydrates and Amino Acids: Monomers to Polymers

Carbohydrates and proteins are built from monomers (simple sugars and amino acids, respectively) that form polymers (polysaccharides and polypeptides/proteins). These macromolecules are crucial for energy storage, structure, and function.

Proteins: Regulation and Response

Proteins are versatile biomolecules that catalyze biochemical reactions (as enzymes), provide structural support, and regulate cellular processes. They also enable cells to respond to environmental changes.

Energy Storage and Use

Cells convert energy from sunlight or organic compounds into ATP (adenosine triphosphate), which is used to power cellular work. Both autotrophs (using sunlight) and heterotrophs (using organic molecules) rely on this process.

Self-Replication and Evolution

Self-Replication

All biomolecules contribute to the ability of life to replicate itself. This property is fundamental to the continuity of life and is most clearly seen in the process of cell division and reproduction.

Evolution

Evolution is defined as the change in heritable characteristics of biological populations over successive generations. This process is driven by genetic variation, natural selection, and other mechanisms.

The Cell: The Basic Unit of Life

Definition and Essential Features

The cell is the smallest unit that meets all the properties of life. All organisms are composed of one or more cells, which carry out the essential functions necessary for life.

Types of Cells

Cells are classified into two main types: prokaryotic and eukaryotic.

Are Viruses Alive?

Viruses exhibit some but not all properties of life. They can store and transmit information, evolve, and respond to their environment, but they lack independent metabolism and cannot self-replicate without a host cell. Thus, their status as living entities is debated.

Summary and Course Objectives

• Practice designing experimental controls.

• Understand that the definition of "living" can vary.

• Recognize the course definition of life.

• Identify the roles of biomolecules (lipids, nucleic acids, proteins, carbohydrates) in supporting life.

• Know that cells are the fundamental units of life.

• Distinguish between types of cells and compare their features.